The Silent Killer

Hybrids are so quiet that pedestrians never hear them coming. Now automakers are racing to make the car of the future sound like the gas guzzlers of old.

The quiet engine of hybrid and electric cars at low speeds poses a risk to pedestrians

Jed Leicester/Getty Images.

Forget gas mileage: The most striking aspect of the new Ford Focus Electric is what it doesn't have. "Battery-powered cars are intrinsically quiet, the motor sound falling between a whir and a whisper," marvels a New York Times review of the car. "But the Focus is deep-space silent, the quietest of the many electric cars I’ve driven."

And that, it turns out, is a problem. Thanks to the Pedestrian Safety Act of 2010, by this summer the National Highway Traffic and Safety Administration is required to initiate a rulemaking process for minimal vehicle noise—not how quiet, but how loud a car must be. That's because NHTSA studies in 2009 (pdf) and 2011 (pdf) confirmed what many long suspected: Hybrids and electric cars are too quiet for the blind or even the fully sighted to hear them coming. Though the NHTSA found little statistically significant difference in collisions over 35 mph—when wind and tire noise negate the difference in engine noise—at lower speeds, hybrids and electric vehicles are 37 percent more likely to hit walkers and 66 percent more likely to collide with cyclists than traditional gas-powered cars.

The victims didn't hear it coming—but did automakers? As counterintuitive as adding car noise may seem, we've long had comparable safety laws in place: For instance, we add foul-smelling Butanethiol to natural gas so that it doesn't sneak up on us in our homes. But there's an even more apt comparison: sleigh bells. Back in the age of real horsepower, the jingling of bells had little to do with winter cheer, and plenty to do with not getting trampled to death. As early as 1797, Baltimore slapped one-dollar fines on anyone who didn't make their sleighs noisy enough. Other cities followed suit, and even the future Motor City had a tough sleigh-bell ordinance that could land silent sleigh drivers in jail.

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The problem that electric cars posed was apparent from the dawn of the motor industry, when primitive gas and electric vehicles were already battling for primacy. As early as 1900, journalist Cleveland Moffett was hailing the electric car as "the automobile of the future"—a status it has held ever since—in no small part due to it being "free from noise." A contemporary electric car guidebook noted that construction had already advanced to the point where noise was "scarcely perceptible." But by 1908, an electric car guide warns "with the silent electric car, especial care is needed to avoid running down incautious pedestrians." After the death of a pedestrian that same year, one EV driver was moved to write tothe Commercial Motor magazine with the question that has haunted the industry ever since: "Is Some Noise Desirable?":

I would like to raise the question as to the expediency of noiselessly running motor vehicles. Not that I wish to commend the present terrible clatter of some of them; but, so much having been made of this quality of noiselessness by the electric-vehicle people in particular, I will so far as to assert that the worship of noiselessness will result in motor vehicles becoming too quiet.

In the absence of much regulation, automakers responded with ... well, bells. Newspaper columnist Frederick Othman marveled at driving a Rauch-Lang Electric Brougham through St. Louis in 1916: "you went silently like a panther. ... [A pearl button] caused a tinkle, like a peculiarly melodious doorbell. The car was so quiet that it was inclined to sneak up on pedestrians, and scare 'em. So there was a good deal of tinkling."

Though electric cars were to disappear under a sea of petroleum for the next 60 years, even a brief resurgence of interest in 1964 spurred the Long Beach Press-Telegram to note that pedestrians would soon need "agility and good peripheral vision." When the oil shocks of the 1970s hit, the renewed interest in EVs quickly revealed the problem again, with one 1979 Department of Energy report generating nationwide headlines of "Electric Cars Too Quiet?"

Automakers were not exactly helpless to respond. The ill-fated Solargen Electric Motor Car Company was already selling electric-conversions of the AMC Concord which were "remarkably silent," as the Syracuse Post-Standard put it, "the only noticeable sound being an electrical 'whine' intentionally engineered into the design to warn pedestrians during acceleration of up to 18 mph." The following year, the equally ill-fated Amectran Exar-1 boasted "a noise generator that emits a harmonic tone at speeds under 30 mph." In Pennsylvania, when a Gettysburg-area power company used modified electric Dodge Omnis, Chevrolet Citations, and Volkswagen Rabbits, "a noise generator was added to alert pedestrians."

Despite these efforts, and years of complaints by the National Federation of the Blind—Honda was aware enough of the problem to file a 1994 patent for an EV noise-generator—automakers could not or would not hear the problem creeping up behind them. The complaints became harder to ignore when, presaging the NHTSA collision findings the next year, studies in 2008 from UC-Riverside and from Western Michigan University showed electric vehicles are hard to hear at low speeds.

The response of the industry was clumsy. Many, including Honda and high-end manufacturer Tesla Motors, doggedly continued to manufacture hybrid and electric cars that ignored the issue. One motive for Tesla becomes apparent when you read their 2011 SEC filings: The safety feature "could negatively impact consumer interest in our vehicles." Nissan Leafs made a half-hearted effort by installing a grating boop-beep sound—but featured a mute button, something the new law wouldn't allow. Toyota and Hyundai have been more proactive: This 2010 Japanese video shows Toyota tinkering with the Jetsons-style sound that is now standard on 2012 Priuses.

The most likely sound of the future, though, may be the sound of the past. Advocates for the blind have long asked for sounds that mimic other cars, and a recent NHTSA study (pdf) shows that simulated conventional engine noises can effectively warn pedestrians at lower overall volumes than conventional vehicles. Audi's new R8 eTron sound, for instance, emits a familiar growl. Whichever standard emerges, by 2017 new hybrids and electric cars will need federally mandated noisemakers installed—and, in a little-reported catch in the law's language, by then the NHTSA may already be moving on extending the law to all cars that run too quietly, no matter what kind of engine they use.

But that still leaves a fleet of over 1 million quiet cars already on the road. This includes the new "deep space quiet" Focus Electric: Ford says it won't install warning units on the ones now shipping out. "We just don't want to be too hasty," one executive informed the Autotrader website.

Considering that they've now had about a century to solve this problem, perhaps they can avoid haste with a tried-and-true solution: Might we suggest the sound of sleigh bells?

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